The present invention relates to a refrigerant power plant with an LNG heat sink, where LNG means "liquefied natural gas". To be more precise, the present invention concerns a novel power generation system that uses a refrigerant as a working fluid which is subjected to cooling by LNG directly or indirectly, pressurized by compressors, vaporized by heating, and which expands to drive turbines and generates electric power.
Some industrialized countries are poor in domestic energy resources. Japan, for example, imported 16.8 million tons of LNG (-162.degree. C.) and 10 million tons of liquefied petroleum gas (-42.degree. C.) in 1980 and is expected to consume more than 40 million tons of LNG every year in the near future. In such a country, gasification plants for LNG use an LNG-vaporizer of the combustion type where LNG flowing inside stainless steel tubes is vaporized and heated toward ambient temperature in a water bath warmed by the combustion gas from a submerged burner. Unfortunately, the LNG-vaporizer of this type consumes fuel in the amount of 2% of the product natural gas and is used only for on the spot inland service or for adjusting the load quickly to cover a sudden increase in need, i.e. for meeting the peak load.
For the base load, current gasification plants use sea or river water as a heat source to keep their running cost low, but these plants also have some drawbacks. First, they cause significant cooling of the surrounding sea or the river water which impacts the ecology therein. Second, their vaporizer works at high pressures, such as 70 kg/cm2, of LNG and pumping devices for it are difficult to maintain and are quite expensive because they have to work at extremely low temperatures. Last but not the least, a considerable amount of energy must be expended to pump and heat LNG. Preferably, an optimum power should be recovered when gasifying LNG because so much power was expended when the liquid state of natural gas was realized.
The present invention aims at moderating the heat pollution caused by the exhaust heat of a conventional steam power plant and the cold pollution caused by the exhaust cold from a gasification plant of LNG. To make clear the contribution this invention has on the energy problem, particularly the heat pollution problem on rivers and in seas, and to understand the motivation and background of the invention, reference is made to the above-mentioned copending U.S. Pat. Application No. 973,735.